The high court's 5-4 decision was limited to the California ban, which became law in November 2008 after a five-month period when gay marriages were legal in the state. The justices ruled that the ban's architects didn't have the right to appeal lower court rulings striking down the prohibition of same-sex unions.
In a related decision Wednesday, the Supreme Court ruled that partners in gay marriages have the same right to federal benefits that heterosexual couples receive.
California officials will likely use the Supreme Court ruling to allow the resumption of same-sex marriages in about a month's time, according to published reports.
Wednesday's decision has no impact on laws in other states banning same-sex marriages.
Right now, gay marriage is legal in the District of Columbia and a dozen states, including Massachusetts, Minnesota, New York and Washington. A few other states legally recognize civil unions or domestic partnerships, but the majority of states -- three dozen in all -- have bans on same-sex marriage.
Whatever happens going forward, a growing body of research suggests that state laws on gay marriage have implications for people's mental and physical health.
When people think of the health aspect of the gay marriage debate, they think of concerns like access to health insurance, said Brian Mustanski, associate professor of medical social science at Northwestern University Feinberg School of Medicine in Chicago.
"People usually get the health insurance issue, but the idea that stigma [related to bans on gay marriage] has direct health effects is something that people may never have considered," Mustanski said.
Richard Wight, a researcher at the University of California, Los Angeles School of Public Health, said his research has suggested that legal unions, particularly marriage, could be a boon to gay and bisexual people's mental health. In a study published in December, Wight's team found less "psychological distress" among same-sex couples in California who got married in the short time window in 2008 when gay marriage was legal in the state.
That was in comparison to gay, lesbian and bisexual Californians who were not in legalized unions. There were no major mental health differences between same-sex couples in legal unions and their married heterosexual counterparts, Wight said.
That was also true of gay people in domestic partnerships, which have been an option for same-sex couples in California since 2000. But marriage, in particular, showed a stronger statistical link to better mental health, he said.
"This shows us there is something going on there," Wight said. You can't conclude, from those findings alone, that the right to marry boosts gay people's mental health, he noted. But his team did try to factor in some of the "usual suspects" in mental health -- such as age, income and education -- and the link between legal unions and less distress remained.
The findings, which appeared in the American Journal of Public Health, were based on a statewide survey of more than 47,000 Californians. It gauged people's psychological distress by asking them how often they'd felt nervous, hopeless, restless or depressed in the past month.
In general, people in legal unions -- whether same-sex or heterosexual marriage, or domestic partnerships -- fared better than single people, regardless of sexual orientation. But the highest distress levels were seen among gay, lesbian and bisexual Californians not in legal unions.
A limit of the study, Wight acknowledged, was that it was conducted at one point in time. So it's not clear what the survey respondents' mental health was like before they got married or entered a domestic partnership. Maybe happier people -- straight or gay -- are more likely to settle down.
But Mustanski said there's also evidence from long-term research that the option to marry affects gay Americans' health.
He pointed to a 2010 study by Columbia University researchers that surveyed nearly 35,000 Americans for about five years. During that time, some U.S. states instituted bans against gay marriage.
The study found that after those bans took effect, rates of anxiety, depression and alcohol use increased among gay, lesbian and bisexual residents. Generalized anxiety disorder -- which refers to chronic worry and tension -- more than doubled in prevalence.
In contrast, psychiatric disorders either held steady or rose a much smaller degree among heterosexuals living in those states.
"I think that's the most compelling evidence we have that there are negative health effects," Mustanski said.
As for why a ban on gay marriage would affect people's mental well-being, Mustanski thinks such laws "send a message that you're a second-class citizen."
"We know that stigma is bad for people," he said. "That's something I think any human being can identify with."
A number of medical groups, including the American Psychological Association and the American Medical Association, have said that barring same-sex couples from civil marriage has negative health effects. And earlier this year, the American Academy of Pediatrics (AAP) threw its support behind gay marriage, saying it's in the best interests of children of same-sex couples.
Not everyone agrees with the endorsements of gay marriage.
Loren Marks, a professor at Louisiana State University, published a review last year in Social Science Research that criticized much of the evidence base for the AAP and other groups' stance on children's well-being. It said that of 59 widely cited studies, almost half looked only at children raised by same-sex couples and had no "heterosexual comparison group." And in many other studies, researchers compared same-sex couples' children with those raised by single mothers.
Ryan Anderson, a fellow at the conservative think-tank the Heritage Foundation, pointed to Marks' findings as one example of the flaws in research looking at children of same-sex parents.
"The science on this is still in its infancy," Anderson said, adding that it's "premature" for scientific groups to support gay marriage based on that research.
"What we do know from years of social science data," Anderson said, "is that children tend to do best when they're raised by their two biological parents -- not just two parents."
He added that while research on single mothers gives some idea of how children fare with no father, there's little data on "what it's like to grow up without a mom."
As for whether marriage, itself, has benefits for gay adults' well-being, the jury is still out, Wight acknowledged. Studies have looked at heterosexual married couples for decades, but there is relatively little data on same-sex couples.
Based on what's known from research on heterosexuals, both married couples and lifelong singles tend to fare best as far as mental and physical health, according to Wight. "It's the people who are divorced, separated or widowed who are worst off," he said.
Of course, those are generalizations, Wight stressed. Someone stuck in a bad marriage may well be worse off than someone who got out of a bad marriage.
But whether marriage is a health boon or not, Wight said that at least having the option to marry could be good for gay and lesbian Americans' well-being. "If there are laws that are actually harmful to mental health, as the evidence suggests, then that's a public health issue," he said.
The U.S. Centers for Disease Control and Prevention has more on gay, lesbian, bisexual and transgender health.